1. Field
Example embodiments relate to an oxide semiconductor obtained by adding a new material to zinc oxide (ZnO), and a thin film transistor (TFT) including the same.
2. Description of the Related Art
Thin film transistors (TFTs) are used in various application fields, for example, as switching and driving devices of display apparatuses and as selection switches of cross-point type memory devices.
Currently, while liquid crystal display (LCD) apparatuses are mainly used as display panels in televisions (TVs), a relatively large amount of research on organic light-emitting display (OLED) apparatuses that may also be applied to TVs is being conducted. TV display technologies are being developed according to demands of the market. Such demands include demand for large-scaled TVs or digital information display (DID) apparatuses, lower price, and high definition (high resolution, improved color rendition, brightness, contrast characteristics, and high color reproducibility). In order to satisfy these demands, substrates, e.g., glass substrates, are required to become larger, and TFTs used as switching and driving devices of display apparatuses are required to have a higher performance.
An example of a TFT used as a switching or driving device of a display apparatus is an amorphous silicon (a-Si) TFT which may be uniformly formed on a large substrate over 2 m in length at a lower cost, and is the most widely used TFT. However, TFTs are required to have improved performance as display apparatuses require high-definition characteristics and larger sizes, and thus, the display apparatuses are regarded as being limited by the operating capabilities of typical a-Si TFTs having a mobility of about 0.5 cm2/Vs. Thus, a high-performance TFT having a higher mobility than an a-Si TFT, and a technology of manufacturing the high-performance TFT are required.
A polysilicon (poly-Si) TFT having a much higher performance than an a-Si TFT has an increased mobility of several tens to several hundred cm2/Vs, and thus, may have a sufficiently high performance to be applied to high-definition display apparatuses which are not easily implemented by using a-Si TFTs. Also, poly-Si TFTs have less device characteristic deterioration than a-Si TFTs. However, the process of manufacturing poly-Si TFTs is more complicated than that of a-Si TFTs, and thus, additional costs increase. Although a poly-Si TFT may be appropriately applied to a high-definition display apparatus or an OLED apparatus, application of poly-Si TFTs is limited due to increased costs compared with a-Si TFTs. Also, poly-Si TFTs have not been implemented on relatively large substrates over 1 m in size until now due to manufacturing equipment limitations or uniformity defects, and thus, may not be easily applied to TV products.
Accordingly, a TFT having advantages of both a-Si TFTs and poly-Si TFTs is required, and research is being actively conducted into such a TFT. A representative example of such a device is an oxide semiconductor device. Among oxide semiconductor devices, zinc oxide (ZnO)-based TFTs are currently attracting attention. ZnO-based materials, e.g., ZnO, indium-zinc oxide (IZO), or ZnO or IZO in which, for example, gallium (Ga), magnesium (Mg), aluminum (Al), or iron (Fe) is doped, have been introduced. A ZnO-based semiconductor device may be manufactured through a low-temperature process and has an amorphous phase, and thus, may be more easily implemented on a relatively large substrate. Also, a ZnO-based TFT has increased mobility and has an improved electric characteristic similar to the poly-Si TFT. Currently, research is being conducted in order to use an oxide semiconductor material layer having increased mobility, for example, a ZnO-based material layer, in a channel area of a TFT.